# 9/19/06 Hofstra University – Overview of Computer Science, CSC005 1 Combinational Circuits Gates are combined into circuits by using the output of one.

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9/19/06 Hofstra University – Overview of Computer Science, CSC005 1 Combinational Circuits Gates are combined into circuits by using the output of one gate as the input for another

9/19/06 Hofstra University – Overview of Computer Science, CSC005 2 Combinational Circuits Because there are three inputs to this circuit, eight rows are required to describe all possible input combinations This same circuit using Boolean algebra is (AB + AC)

9/19/06 Hofstra University – Overview of Computer Science, CSC005 3 Now let’s go the other way; let’s take a Boolean expression and draw Consider the following Boolean expression A(B + C) Now compare the final result column in this truth table to the truth table for the previous example They are identical

9/19/06 Hofstra University – Overview of Computer Science, CSC005 4 Now let’s go the other way; let’s take a Boolean expression and draw We have therefore just demonstrated circuit equivalence That is, both circuits produce the exact same output for each input value combination Boolean algebra allows us to apply provable mathematical principles to help us design logical circuits

9/19/06 Hofstra University – Overview of Computer Science, CSC005 5 Homework Read Chapter Four, Sections 4.4 – 4.7 Exercise: P119-120, 55 & 59

9/19/06 Hofstra University – Overview of Computer Science, CSC005 6 Chapter 5 Computer Components

9/19/06 Hofstra University – Overview of Computer Science, CSC005 7 Communication Application Operating System Programming Hardware Information Layers of a Computing System

Hofstra University – Overview of Computer Science, CSC005 8 Chapter Goals Read an ad for a computer and understand the jargon List the components and their function in a von Neumann machine Describe the fetch-decode-execute cycle of the von Neumann machine

Hofstra University – Overview of Computer Science, CSC005 9 Chapter Goals Describe how computer memory is organized and accessed Name and describe different auxiliary storage devices Define three alternative parallel computer configurations

Hofstra University – Overview of Computer Science, CSC005 10 Computer Components Consider the following ad

Hofstra University – Overview of Computer Science, CSC005 11 Sizes in Perspective Admiral Grace Murray Hopper A coil of wire nearly 1,000 feet long Distance traveled by an electron along the wire in the space of a microsecond A short piece of wire In the space of a nanosecond A bag containing grains of pepper In the space of a picosecond

Hofstra University – Overview of Computer Science, CSC005 12 Sizes in Perspective

Hofstra University – Overview of Computer Science, CSC005 13 Stored-Program Concept Figure 5.1 The von Neumann architecture Von Neumann Bottleneck

Hofstra University – Overview of Computer Science, CSC005 14 John von Neumann Hungrain born mathematician Orignal member of Institute of Advanced Studies at Princeton where he met Alan Turing Member of the Manhattan Project Responsible for modern computer design – the “stored – program computer” Fly and the Train Problem!

Hofstra University – Overview of Computer Science, CSC005 Memory Memory is a collection of cells, each with a unique physical address

Hofstra University – Overview of Computer Science, CSC005 16 Arithmetic/Logic Unit Performing basic arithmetic operations such as adding Performing logical operations such as AND, OR, and NOT Most modern ALUs have a small amount of special storage units called registers

Hofstra University – Overview of Computer Science, CSC005 17 John Vincent Atanasoff Native of Hamilton, NY Envisioned a computer device that was “digital” The idea of building an electronic digital computer came to him while he was sitting in a tavern – first computer insomniac 1939, the Atanasoff Berry Computer (ABC) at University of Iowa Forgotten “Father of the Computer”

Hofstra University – Overview of Computer Science, CSC005 18 Input/Output Units Input Unit A device through which data and programs from the outside world are entered into the computer Keyboard, the mouse, and scanning devices Output unit A device through which results stored in the computer memory are made available to the outside world Printers and video display terminals

Hofstra University – Overview of Computer Science, CSC005 19 Herman Hollerith Developed calculating method for 1890 census Based on Hollerith code using card with holes punched in them 1896 founded the Tabulating Machine Company 1911 merged with another company to form the Computing Tabulating Recording (CTR) company, with Thomas J Watson president 1924 company renamed IBM

Hofstra University – Overview of Computer Science, CSC005 20 Control Unit Control unit The organizing force in the computer There are two registers in the control unit The instruction register (IR) contains the instruction that is being executed The program counter (PC) contains the address of the next instruction to be executed ALU and the control unit called the Central Processing Unit, or CPU

Hofstra University – Overview of Computer Science, CSC005 21 Flow of Information The parts are connected to one another by a collection of wires called a bus Figure 5.2 Data flow through a von Neumann architecture

Hofstra University – Overview of Computer Science, CSC005 22 The Fetch-Execute Cycle Fetch the next instruction Decode the instruction Get data if needed Execute the instruction

Hofstra University – Overview of Computer Science, CSC005 23 Figure 5.3 The Fetch-Execute Cycle

Hofstra University – Overview of Computer Science, CSC005 24 RAM and ROM RAM stands for Random Access Memory Inherent in the idea of being able to access each location is the ability to change the contents of each location ROM stands for Read Only Memory The contents in locations in ROM cannot be changed RAM is volatile, ROM is not This means that RAM does not retain its bit configuration when the power is turned off, but ROM does

Hofstra University – Overview of Computer Science, CSC005 25 Secondary Storage Devices Because most of main memory is volatile and limited, it is essential that there be other types of storage devices where programs and data can be stored when they are no longer being processed Secondary storage devices can be installed within the computer box at the factory or added later as needed

Hofstra University – Overview of Computer Science, CSC005 Magnetic Tape The first truly mass auxiliary storage device was the magnetic tape drive Figure 5.4 A magnetic tape 5-17

Hofstra University – Overview of Computer Science, CSC005 Tape Silo Handled by a robot Travels 80 mph

Hofstra University – Overview of Computer Science, CSC005 Magnetic Disks A read/write head travels across a spinning magnetic disk, retrieving or recording data Figure 5.5 The organization of a magnetic disk

Hofstra University – Overview of Computer Science, CSC005 A Hard Drive In Action Inside A Hard DriveInside A Hard Drive - Simple operations performed by a hard drive with no cover, so that you can see what it looks like inside. This experiment was performed on an old hard drive, do not try this with newer expensive hard drives, it is a bit risky. -from digg.comdigg.com What Happens When You Drop A DIsk - Or Two!

Hofstra University – Overview of Computer Science, CSC005 30 Compact Disks A CD drive uses a laser to read information stored optically on a plastic disk CD-ROM is Read-Only Memory DVD stands for Digital Versatile Disk

Hofstra University – Overview of Computer Science, CSC005 31 USB Drive Flash Drive is a form of non-volatile memory Stores information in an array of floating gate transistors, called "cells"

Hofstra University – Overview of Computer Science, CSC005 32 Touch Screens Touch screen A computer monitor that can respond to the user touching the screen with a stylus or finger There are four types Resistive Capacitive Infrared Surface acoustic wave (SAW)

Hofstra University – Overview of Computer Science, CSC005 33 Touch Screens Resistive touch screen A screen made up of two layers of electrically conductive material. One layer has vertical lines, the other has horizontal lines. When the top layer is pressed, it comes in contact with the second layer which allows electrical current to flow. The specific vertical and horizontal lines that make contact dictate the location on the screen that was touched.

Hofstra University – Overview of Computer Science, CSC005 34 Touch Screens Capacitive touch screen A screen made up of a laminate applied over a glass screen. The laminate conducts electricity in all directions, and a very small current is applied equally on the four corners. When the screen is touched, current flows to the finger or stylus. The location of the touch on the screen is determined by comparing how strong the flow of electricity is from each corner.

Hofstra University – Overview of Computer Science, CSC005 35 Touch Screens Infrared touch screen A screen with crisscrossing horizontal and vertical beams of infrared light Sensors on opposite sides of the screen detect the beams. When the user breaks the beams by touching the screen, the location of the break can be determined.

Hofstra University – Overview of Computer Science, CSC005 36 Touch Screens Surface acoustic wave (SAW) A screen with crisscrossing high frequency sound waves across the horizontal and vertical axes. When a finger touches the surface, the corresponding sensors detect the interruption and determine the location of the touch.

Hofstra University – Overview of Computer Science, CSC005 37 Synchronous processing One approach to parallelism is to have multiple processors apply the same program to multiple data sets Figure 5.7 Processors in a synchronous computing environment

Hofstra University – Overview of Computer Science, CSC005 38 Pipelining Arranges processors in tandem, where each processor contributes one part to an overall computation Figure 5.8 Processors in a pipeline

Hofstra University – Overview of Computer Science, CSC005 39 Independent Processing with Shared Memory Figure 5.9 A shared-memory configuration of processors

9/19/06 Hofstra University – Overview of Computer Science, CSC005 40 Assignment One Let Me Know If I Can Publish On Web Site There Is No Obligation

9/19/06 Hofstra University – Overview of Computer Science, CSC005 41 Homework Read Chapter Five, All Sections

9/19/06 Hofstra University – Overview of Computer Science, CSC005 42 Mid-Term Take Home Exam – Non-Trivial (think!) Cover Chapters 1-5 & 16 & Anything Covered In Class Given Out: Oct 11 Due Back: Oct 18 No Lateness!!!

9/19/06 Hofstra University – Overview of Computer Science, CSC005 43 Good Night and Good Dreams!

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